Transmission of asynchronous data in a synchronous channel is that the asynchronous data is converted into synchronous data for transmission in a quasi-synchronous channel, and the data in the quasi-synchronous channel is received without damage, and the data is then restored to the asynchronous data. In general, the transmission of the asynchronous data in the synchronous channel has low requirements on the clock, and since there is idle data between asynchronous data packages, which can offset the deviation between the clock frequencies of baud rate generators of the transmitting end and the receiving end, i.e. both the transmitting end and the receiving end can obtain the same baud rate as that of the asynchronous data by using the frequency division of the local oscillator to sample the asynchronous data. However, if the asynchronous data is transmitted continuously for a long time, i.e. there is no idle between data, for example, a Personal Computer (PC) uses a serial port to continuously transmit a large number of pictures or documents and so on, there will generate clock sliding on the channel over time, which results in error of code elements in the transmission. Although increasing the buffer of the receiving end can enhance the anti-slip property, it is also very easy to result in completely writing and reading the buffer over time. A Chinese Patent CN200720102430.X provides a method for inserting or deleting empty blocks to implement synchronous transmission of asynchronous data; however, such method is very complex, and requires that the transmitted and received clocks of the baud rate generators are completely synchronous.